Variable intensity illuminator

ABSTRACT

Variable illumination apparatus includes means for closely controlling the voltage to a lamp so that low values of illumination can be readily adjusted. The frequency of an astable multivibrator is adjusted through a potentiometer coupling the astable multivibrator to a voltage source. Each pulse from the astable multivibrator drives a monostable multivibrator into its quasi-stable state. The time that the monostable multivibrator remains in the quasi-stable state is adjusted by the same potentiometer that adjusts the frequency of the astable multivibrator in such a way that the quasi-stable time duration increases as the pulse repetition rate of the astable multivibrator increases. The circuit is proportioned so that the quasi-stable pulse duration is longer than the pulse repetition period of the astable multivibrator when the astable multivibrator is operating at its maximum rate, so that under these conditions the monostable multivibrator is clamped in its quasi-stable state. The load is taken from the complementary output terminal of the monostable multivibrator so that lamp voltage decreases to zero as the repetition rate and pulse duration is increased.

O United States Patent 1191 [111 3,821,600 Wesner 5] June 28, 1974 VARIABLE INTENSITY ILLUMINATOR Primary ExaminerAlfred L. Brody [75] Inventor: Charles R. Wesner, Crozet, Va. fi g' ifl or Flrm H0ward Terry; Joseph I 0e [73] Assignee: Sperry Rand Corporation, New

57 ABSCT [22] Filed: June 1972 Variable illumination apparatus includes means for [21] Appl. No.: 267,342 closely controlling the voltage to a lamp so that low values of illumination can be readily adjusted. The frequency of an astable multivibrator is adjusted through a potentiometer coupling the astable multivibrator to [52] Cl 53 5 457 a voltage source. Each pulse from the astable multivi- 5 l I t Cl b 1/02 brator drives a monostable multivibrator into its quasi- E d 298 stable state. The time that the monostable multivibra- 1e 3 g f'g6; 65 tor remains in the quasi-stable state is adjusted by the 274 I5 4 9 4 same potentiometer that adjusts the frequency of the astable multivibrator in such a way that the quasistable time duration increases as the pulse repetition rate of the astable multivibrator increases. The circuit [56] References Cited is proportioned so that the quasi-stable pulse duration UNITED STATES PATENTS is longer than the pulse repetition period of the astable 3 19] 07] 6/1965 King et al 307/271 X multivibrator when the astable multivibrator 1s operat- 3 342 948 9/1967 Knauer a51111111111111111111.. 332 14 x ing at its maximum rate the! under these Condi- 3:383:546 5/1963 chopey 7 7 x tions the monostable multivibrator is clamped in its 3,492,593 1/1970 Ullmann et a1. 307/273 X quasi-stable state. The load is taken from the comple- 3,514,668 5/1970 Johnson et al 3 15/307 X mentary output terminal of the monostable multivibra- 3,568,094 3/l97l Metzger 332/l4 X tor so that lamp voltage decreases to Zero as the rapetition rate and pulse duration is increased.

5 Claims, 4 Drawing; Figures VC(L 9 17 f 23 D l M BRIGHT 11 13 o o f i x M o N o ASTABLE STABLE Niki/GER 11 27 25 1 ["1 1' u 'LFLF m Pmmmma r974 SHEET 2 BF 2 mm h K N In jmm VARIABLE INTENSITY ILLUMINATOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to variable illumination-apparatus and more specifically to pulse type variable illumination devices.

2. Description of the Prior Art Situations arise where the brightness of a lamp must be controllable at very low light levels.

Navigation instruments used on shipboard, for instance, must be illuminated for night viewing. The brightness of such illumination must be readily adjustable down to very low levels depending on the ambient light so as to permit the various instruments to be read without distraction.

Lamp dimmers employing conventional rheostats are not suitable for such purposes. Solid state devices which provide a variable pulse width for controlling lamp brightness have been devised. However, such devices typically provide pulse durations which vary only within a range of about 100 percent to 12 percent. The minimum brightness obtainable. with such devices is often too great for night viewing.

SUMMARY OF THE INVENTION Thelamp in a variable illumination apparatus is energized from pulse forming networks which simultaneously vary the period and pulse width of the complementary output pulse train from a monostable multivibrator so as to provide an extremely wide range of brightness.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, an astable multivibrator 11 provides a rectangular output pulse train V which triggers a monostable multivibrator 13 so as to produce an output pulse train V,,,. The output pulses from the astable multivibrator may typically have durations in the order of 40 nanoseconds. The pulse repetition rate of the astable multivibrator is determined by the R-C network which includes the capacitor 15, the series resistor l7 and a portion of the potentiometer resistance element 19. The durationof the pulses in the output pulse train from the monostable multivibrator 13 is determined by the RC network including the capacitor 21, the series resistor 23 and a portion of the potentiometer resistance element 19. Both multivibrators are energized from a suitable voltage source V through the respective R-C networks.

The monostable multivibrator l3 normally remains in its stable state until triggered by the trailing edge of a pulse from the astable multivibrator whereupon it is switched to its quasi-stable state. The monostable multivibrator remains in this quasi-stable state for a period of time determined by the associated R-C network.

The output pulse train V,,, is taken from the complementary output terminalOso that a high level voltage appears only when the monostable multivibrator is in its stable state. The pulse train from theO terminal is applied to the lamp 25 through a conventional amplifier 27. The lamp, in turn, is connected to a voltage source having a value equivalent to the high level voltage from the amplifier.

The time constant of the R-C network associated with the astable multivibrator determines the pulse repetition rate of this multivibrator. Thus when the adjust able arm of the potentiometer is moved toward the astable multivibrator, the time constant of the RC network is decreased and the pulse repetition rate of the astable multivibrator increases. Similarly, the time con stant of the R-C network associated with the monostable multivibrator determines the duration of the quasistable state in this multivibrator so that when the ad justable arm of the potentiometer is moved away from the monostable multivibrator, the duration of the quasi-stable state is increased.

The interaction of the two multivibrators as the potentiometer setting is changed can be better understood by referring to FIGS. 2 and 3. FIG. 2 represents typical waveshapes which might be expected when the adjustable arm of the potentiometer has been moved toward the right in FIG. I so as to produce a relatively bright illumination, whereas FIG. 3 represents typical waveshapes which might be expected when the adjustable arm of the potentiometer is moved toward the left so as to provide a lower level of light output.

Referring more specifically to FIG. 2, the output pulse train V,, from the astable multivibrator consists of a train of pulses 29 separated by a relatively long interpulse intervals 31. The trailing edge of each pulse in the train V switches the monostable multivibrator to its quasi-stable state so as to produce a high level output signal at the Q output terminal of the monostable multivibrator. However, the lamp 25 of FIG. 1 is energized in response to the complementary output signal from the monostable multivibrator as represented by the pulse train V,,,. As indicated in FIG. 2, the pulse train V,,, has a relatively high duty cycle in that a high level voltage is produced for relatively long periods of time.

the potentiometer has increased the quasi-stable period of the monostable multivibrator. The complementary pulses V,, from the monostable multivibrator'now form a train of relatively short pulses so that this pulse train now has a low duty cycle. Very little energy is supplied to the lamp 25 over a given period of time.

It will be appreciated that FIGS. 2 and 3 represent intermediate conditions. That is, the potentiometer can be adjusted well beyond the conditions represented by these figures so as to produce pulse trains V,, having higher and lower duty cycles respectively. In particular, the R-C network associated with the monostable multivibrator is proportioned so that. movement of the adjustable potentiometer arm toward the left in the circuit of FIG. 1 can increase the quasi-stable time dura' tion of the monostable multivibrator pulses to such a degree that they exceed the corresponding interpulse interval of the V,, pulse train. Under these conditions, the monostable multivibrator is clamped in the quasistable state and the Q (true) voltage remains at a high level. Thus the true output of the monostable multivi-. brator can be varied from a minimum condition in which short pulses at a low repetition rate are produced to a condition in which a steady dc. voltage is produced.

The critical range of operation of instrument panel dimmer circuits is in the lower illumination levels; therefore, the desired degree of control is achieved according to the principles of the present invention by energizing the lamp as a function of the complementary output of the monostable multivibrator through the 6 terminal. The energy applied to the lamp can be smoothly decreased to a zero level so that the brightness of the lamp can be readily adjusted from a predetermined maximum brightness to complete darkness. A high degree of control is available in the lower illumination levels so that compensation is possible for slight changes in the ambient.

As presently preferred, the circuit of FIG. 1 can be readily implemented by using commercially available semiconductor integrated circuits. Such an embodiment is depicted in FIG. 4 in which a single TTp.L9602 integrated circuit available from the Fairchild Semiconductor Company may provide both the astable and monostable multivibrator sections of the dimmer circuit. The aforementioned integrated circuit is a dc. dual level sensitive re-triggerable, resettable monostable multivibrator. The use of this particular integrated circuit facilitates construction of the dimmer circuit in that the integrated circuit is designed to accept external R-C timing networks. The integrated circuit itself consists of first and second one-shot multivibrators 33 and 35 and input gates 37 and 39.

A preliminary data sheet dated Man, 1970 published by the Fairchild Semiconductor Company describes the construction and operation of this particular integrated circuit and includes a description of a pulsed generator in which a feedback signal around one multivibrator is used to convert this device into an astable multivibrator. The frequency of the astable multivibrator is adjustable by external means and its output signal is used to feed the second multivibrator. The second multivibrator is adjusted by independent external means so as to extend the pulse width to the required value.

In the circuit of HO. 4, the multivibrator 33 is con-- verted to an astable multivibrator by means of a feedback loop 41. The voltage from the output terminal of the multivibrator 33 is applied through a time delay network consisting of a resistor 43 and a capacitor 45 connected to ground. The junction between the resistor 43 and the capacitor 45 is connected to the inverting input terminal of the gate 37. The direct input terminal to the same gate is connected to ground. The resistor 43 and capacitor 45 are selected to increase the output pulse width of the multivibrator 33 to a suitable value. The reset portion of the multivibrator 33 is permanently disabled by coupling the. C pin to a positive voltage source through a suitable series resistor 47.

The Q output of the multivibrator 33 is also applied to the direct input terminal of the gate 39. The inverting input terminal of the gate 39 is maintained at a high logic level through a line 49 which is coupled to the positive voltage source. Thus the OR gate 39 provides a trigger signal to the multivibrator 35 only in response to the Q output voltage of the multivibrator 33. The reset pin C of the multivibrator 35 is also coupled to the positive voltage source through the resistor 47 so as to permanently disable the reset circuit of the multivibrator 35.

The output signal from the multivibrator 35 is t aken from the complementary output terminal Q. The Q output voltage is applied to the lamp 49 through a conventional amplifier 51. The lamp, in turn, is connected to a suitable voltage source.

The illumination of the lamp 49 is controlled through the single potentiometer 53. The adjustable arm of the potentiometer is connected to the V voltage source which is used to energize the multivibrators. One end of the resistance element 55 of the potentiometer is coupled to the multivibrator 33 through a resistor 57 and a capacitor 59. in the particular integrated circuit being considered, the R-C timing elements are connected to the pins designated as l and 2 by the manufacturer.

The other end of the resistance element 55 of the potentiometer 53 is coupled to the multivibrator 35 through a series resistor 61 and a capacitor 63. These connections are made to pins designated as 14 and 15 by the manufacturer.

Operation of the circuit of FIG. 4 is essentially the same as that of FIG. 1. Brightness of the lamp 49 may be increased merely by moving the adjustable arm of the potentiometer 53 towards the right so as to increase and decrease the series resistance of the R-C networks associated with the multivibrators 33 and 35, respectively. As was the case with the circuit of FIG. 1, the aforementioned adjustment to the potentiometer 53 decreases the pulse repetition rate of the astable multivibrator 33 and at the same time decreases the duration of the quasi-stable state of the monostable multiyibrator 35. However, since the load is taken from the Q terminal of the monostable multivibrator 35, the duty cycle of the pulse train applied to the lamp 49 is increased so that the average power applied to the lamp is correspondingly increased. Conversely, when the adjustable arm of the potentiometer 53 is moved towards the left in the diagram of FIG. 4, the average power ap-v plied to the lamp 49 is gradually and smoothly decreased to a level such that the lamp 49 can be completely darkened.

The dimmer circuit of the present invention is particularly valuable in situations such as instrument panel lighting for shipboard or aircraft use where space requirements and electrical isolation problems are particularly acute. In such environments, variable resistance type dimmer circuits are troublesome because of their bulk and interference characteristics. The prior art solid state circuits in which only the pulse width is regulated overcame many of the problems attendant upon the use of variable resistance type dimmers. However, the prior art pulse width circuits suffer because of their relatively narrow control range. The circuit of the present invention provides a convenient, wide range, interference-free device.

Although the invention has been described as utilizing circuits in which the monostable multivibrator is triggered in response to the trailing edges of the pulses from the pulses from the astable multivibrator, it will be appreciated that this feature is merely illustrative. Circuits in which the leading edges of the astable multivibrator pulses actuate the monostable multivibrator may be used where desired.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

1 claim:

1. Wide range, variable illumination apparatus comprising a lamp, monostable multivibrator means, an astable multivibrator coupled to drive said monostable multivibrator means from a stable state into a quasistable state in response to a selected edge of an output pulse from the astable multivibrator, first means to vary the pulse repetition rate of said astable multivibrator, second means to vary the quasi-stable state duration of said monostable multivibrator, said first and second means including a potentiometer having'an adjustable arm connected to a source of d.c. voltage suitable for energizing said multivibrators, said astable multivibrator being coupled to one end of the resistance element of said potentiometer through a first RC means, said monostable multivibrator being coupled to the other end of said resistance element through a second RC means so as to increase and decrease the pulse repetition rate of said astable multivibrator as the quasistable state duration of said monostable multivibrator is simultaneously increased and decreased respectively, said first and second multivibrators being adjusted so that the quasi-stable pulse duration of said monostable multivibrator is at least as long as the interpulse interval of the wave train from said astable multivibrator when the astable multivibrator is operating at its maximum pulse repetition rate, and means to energize said lamp only when the monostable multivibrator is in its stable state.

2. The apparatus of claim 1 wherein said monostable multivibrator has a complementary output terminal and said lamp is coupled to said complementary output terminal.

3. The apparatus of claim 2 wherein said selected edge is the trailing edge.

4. The apparatus of claim 2 wherein the multivibrators are packaged as an integrated circuit in which external R-C networks are used to adjust the pulse repetition rate and quasi-stable states of the astable and monostable multivibrator portions of the integrated circuit, respectively.

5. A wide range variable illumination circuit comprising a lamp, a source of d.c. voltage, an astable multivibrator, first variable R-C network means for coupling said source of dc. to said astable multivibrator, the pulse repetition rate of said astable multivibrator being determined by the resistance and capacitance values of said first network, said first network including a potentiometer having an adjustable arm connected to said d.c. source and a resistance element having one end thereof coupled to said astable multivibrator whereby the pulse repetition rate of said astable multivibrator increases as said adjustable arm is positioned closer to said one end, a monostable multivibrator coupled to said astable multivibrator so as to be driven into its quasi-stable state in response to the trailing edge of a pulse from said astable multivibrator, second variable R-C network means for coupling said monostable multivibrator to said source of d.c. through the other end of said resistance element, said second network being arranged to increase the length of "time that said monostable multivibrator remains in its quasi-stable state as said adjustable arm is moved away from said other end, said first and second networks being proportioned so that said monostable multivibrator remains in its quasistable state for a time period at least as long as the interpulse interval of the pulse train from said astable multivibrator when the astable multivibrator is operating at its maximum pulse repetition rate, and means to energize said lamp only when said monostable multivibrator is in its stable state. 

1. Wide range, variable illumination apparatus comprising a lamp, monostable multivibrator means, an astable multivibrator coupled to drive said monostable multivibrator means from a stable state into a quasi-stable state in response to a selected edge of an output pulse from the astable multivibrator, first means to vary the pulse repetition rate of said astable multivibrator, second means to vary the quasi-stable state duration of said monostable multivibrator, said first and second means including a potentiometer having an adjustable arm connected to a source of d.c. voltage suitable for energizing said multivibrators, said astable multivibrator being coupled to one end of the resistance element of said potentiometer through a first RC means, said monostable multivibrator being coupled to the other end of said resistance element through a second RC means so as to increase and decrease the pulse repetition rate of said astable multivibrator as the quasi-stable state duration of said monostable multivibrator is simultaneously increased and decreased respectively, said first and second multivibrators being adjusted so that the quasi-stable pulse duration of said monostable multivibrator is at least as long as the interpulse interval of the wave train from said astable multivibrator when the astable multivibrator is operating at its maximum pulse repetition rate, and means to energize said lamp only when the monostable multivibrator is in its stable state.
 2. The apparatus of claim 1 wherein said monostable multivibrator has a complementary output terminal and said lamp is coupled to said complementary output terminal.
 3. The apparatus of claim 2 wherein said selected edge is the trailing edge.
 4. The apparatus of claim 2 wherein the multivibrators are packaged as an integrated circuit in which external R-C networks are used to adjust the pulse repetition rate and quasi-stable states of the astable and monostable multivibrator portions of the integrated circuit, respectively.
 5. A wide range variable illumination circuit comprising a lamp, a source of d.c. voltage, an astable multivibrator, first variable R-C network means for coupling said source of d.c. to said astable multivibrator, the pulse repetition rate of said astable multivibrator being determined by the resistance and capacitance values of said first network, said first network including a potentiometer having an adjustable arm connected to said d.c. source and a resistance element having one end thereof coupled to said astable multivibrator whereby the pulse repetition rate of said astable multivibrator increases as said adjustable arm is positioned closer to said one end, a monostable multivibrator coupled to said astable multivibrator so as to be driven into its quasi-stable state in response to the trailing edge of a pulse from said astable multivibrator, second variable R-C network means for coupling said monostable multivibrator to said source of d.c. through the other end of said resistance element, said second network being arranged to increase the length of time that said monostable multivibrator remains in its quasi-stable state as said adjustable arm is moved away from said other end, said first and second networks being proportioned so that said monostable multivibrator remains in its quasi-stable state for a time period at least as long as the interpulse interval of the pulse train from said astable multivibrator when the astable multivibrator is operating at its maximum pulse repetition rate, and means to energize said lamp only when said monostable multivibrator is in its stable state. 